Neuroendocrine cells express high levels of neuropeptide genes and thus are useful models to examine regulation of gene expression in the CNS. We have found that a wide variety of postnatal neuroendocrine cells survive and express specific neuropeptide genes in organotypic slice- explant cultures. Utilizing this model system, we examined the effects of potassium (K+) and estradiol treatment on peptide mRNA levels in LHRH and OT neurons using semiquantitative in situ hybridization histochemistry. Brain slices from postnatal day 5 rats were cultured in serum-containing media to allow thinning, maintained in defined media (serum-free) for 4-6 days, and exposed to either 40 Mm K+ (4 hrs) or 10 nM estradiol (8 or 24 hrs). To determine if the effect of estradiol on peptide gene expression in LHRH and OT cell subtypes was direct or via interneurons, the cultures were examined under "normal" synaptic activity and tetrodoxin activity blockade. Analyses of the OT cultures was performed using X-ray film, providing a density value/culture which corresponds to mRNA levels. Comparisons of these values showed that OT mRNA levels approximately doubled after exposure to 40 mM K+ (p=0.01). Densitometric single cell analyses of LHRH and OT neuronal mRNA levels are currently in progress. Single cell analyses will determine if either of these neuroendocrine cell types contain subpopulations which differentially respond to depolarization and estradiol treatment. Our attempts to tissue culture pedtidergic sensory ganglion cells are relatively homogenous neuronal models for peptide biosynthesis studies are proceeding well. Highly differentiated (postnatal) rat sensory (dorsal root or trigeminal) ganglion cells in culture survive very well for weeks in defined media in the ganglion cells or absence of NGF. In the presence of NGF most of the cultured cells show exaggerated CGRP and substance P coexistence patterns as compared to their in vivo state. These cells in culture appear to be excellent models for the study of mechanisms of selective gene expression and posttranslational mechanisms involved in neuropeptide biosynthesis.